Field of the Invention
This invention relates to electricity and more particularly to an elevated temperature detection and interrupter circuit for a power cable to disconnect electrical power upon the detection of an elevated temperature in an electrical plug or an electrical receptacle to prevent an over heated condition.
Description of the Related Art
The most common method of connecting an electrical appliance to an electric power source is through the use of an electrical power plug inserted into an electrical power source receptacle. The electrical power plug includes a first and a second electrical blade for insertion within a first and a second slot of the power source receptacle. The first and second electrical blades are retained within the first and second slots of the electrical power source receptacle by a resilient slot connector located within the first and second slots of the electrical power source receptacle. The resilient slot connectors located within the first and second slot provides a mechanical engagement between the resilient slot connectors and the inserted first and second electrical blades to enable a low resistance electrical contact therebetween.
In many cases, the mechanical and/or electrical contact between one of the resilient slot connectors and the inserted first and second electrical blades deteriorates thus raising the electrical resistance of the electrical contact therebetween. This deterioration of the mechanical and/or electrical contact between one of the resilient slot connectors and the inserted first and second electrical blades may be caused by a number of reasons.
The deterioration between one of the resilient slot connectors and the inserted electrical blade may be caused by corrosion of either the resilient slot connector and/or the inserted electrical blade. The corrosion of either the resilient slot connector and/or the inserted electrical blade results in an increase in electrical resistance therebetween. Furthermore, the deterioration between one of the resilient slot connectors and the inserted electrical blade may be caused by a loss of resiliency of the resilient slot connectors. The loss of resiliency of the resilient slot connector reduces the mechanical contact between the resilient slot connector and the inserted electrical blade thus raising the electrical resistance of the electrical contact therebetween. In some instances, the mere aging of the electrical power plug and/or electrical power source receptacle may cause a loss of resiliency of the resilient slot connector as well as the corrosion of either the resilient slot connector and/or the inserted electrical blade.
The increase in resistance between the resilient slot connector and/or the inserted electrical blade results in an increase in heat during current conduction through the electrical contact between the resilient slot connector and the inserted electrical blade. The increase in heat further increases the resistance of the electrical contact between the resilient slot connector and the inserted electrical blade resulting in a progressive increase in heat and a progressive increase in electrical resistance. Ultimately, the progressive increase in heat will result in heat, smoking and possibly ignition of the electrical power source receptacle and/or the electrical power plug. Such an ignition may spread to adjacent areas causing loss of property and possibly the loss of life.
U.S. Pat. No. 4,310,837 to Kornrumpf et al. discloses a temperature indicating apparatus for sensing overheating at a pair of terminals on an electrical power line comprising a neon gas-filled glow tube and a thermistor electrically coupled in series across the terminals, with a resistor electrically coupled in parallel with the glow tube. The thermistor is thermally coupled to the terminations so that an excessive temperature rise at either terminal decreases the thermistor resistance to a level at which sufficient voltage appears across the glow tube to ignite the glow tube and provide a visual indication of overheating. The circuit readily lends itself to a plug-in type configuration if the terminals to be monitored are in a duplex receptacle, or to employment in a cube tap.
U.S. Pat. No. 4,470,711 to Brzozowski discloses a temperature indicating apparatus for sensing overheating at a pair of terminals on an electrical power line comprising pair of thermocouples, each thermally coupled to and electrically isolated from a different one of the terminals, and a light emitting diode (LED) coupled to the output of the thermocouples through a conditioning circuit. An excessive temperature rise at either terminal causes the output voltage of the thermocouple coupled thereto to increase, thus causing the LED to be lit and to provide a visual indication of overheating. A meter display may be provided to show the actual temperature of the terminals in response to thermocouple voltage output. A method for determining heating at a termination without physical intervention comprises determining the rate of temperature rise of the termination for a known current therethrough and comparing the rate to a predetermined rate threshold.
U.S. Pat. No. 5,590,010 to Ceola et al. discloses an electric device provided as an interface between a permanent power source (e.g., an electric wall outlet) and an electrical appliance for interrupting electrical power to the appliance in the event the temperature of either the power cord plug of the electrical appliance or permanent power source rises above a predetermined temperature. The electric device detachably couples to the electric power terminals of both the permanent power source and electrical appliance and is sensitive to the temperature of the aforementioned terminals. The electric device includes first and second temperature switching elements which are responsive to interrupt electrical power from the permanent power source to the appliance when either of the terminals is of a temperature which equates with a first predetermined temperature determined by the first temperature switching element or a second predetermined temperature determined by the second temperature switching element.
U.S. Pat. No. 5,600,306 to Ichikawa et al. discloses an electrical receptacle unit including at least one receptacle body internally provided with a pair of slotted terminals for insertion of a pair of blades of a load-side electrical plug. A thermistor is encased in a protective tube outwardly projectable from between the slotted terminals of the receptacle body. A coil spring is provided for projecting the thermistor out from the receptacle body. A relay enables and disables supply of electric power to the slotted terminals. A control circuit operates the relay to cut off supply of electric power to the slotted terminals when the temperature of the thermistor reaches or exceeds a preset temperature. A buzzer is operated by an output signal produced by the control circuit when the temperature of the thermistor reaches or exceeds the preset temperature. When the thermistor rises to or above the preset temperature owing to tracking or the like, supply of power to the load-side plug is cut off and the alarm is activated to produce a warning that the load-side plug has overheated.
U.S. Pat. No. 5,862,030 to Watkins, Jr. et al. discloses an electrical safety device comprising a sensor strip disposed in the insulation of a wire or in the insulation of a sheath enclosing a bundle of insulated electrical conductors. The sensor strip comprises a distributed over temperature sensing portion comprising a conductive polymer having a positive temperature coefficient of resistivity which increases with temperature sufficient to result in a switching temperature. A mechanical damage sensing portion comprises a strip disposed in the sheath in a mechanical damage sensing pattern which becomes damaged or open upon mechanical damage of the sheath before the bundle of conductors are damaged. The over temperature sensing portion and the mechanical damage sensing portion may be the same sensing strip disposed in the sheath and arranged in a helical relationship with a longitudinal axis of the sheath.
U.S. Pat. No. 5,930,097 to Ceola et al discloses an electric device provided as an interface between a permanent power source (e.g., an electric wall outlet) and an electrical appliance. The device operates to interrupt electrical power to the electrical appliance in response to an increase in temperature of either the power cord plug of the electrical appliance or the terminals of the permanent power source to a predetermined temperature. The electric device detachably couples to the electric power terminals of both the permanent power source and the electrical appliance and is sensitive to the temperature at the terminals. The device includes a thermostat which rests on a thermal barrier member in thermal communication with the terminals, and is responsive to heat generated at the terminals to interrupt electrical power from the permanent power source to the appliance.
U.S. Pat. No. 5,945,903 to Reddy et al discloses a circuit protection device including a pair of terminals to be electrically connected into an electrical circuit, a pair of spaced current-carrying extensions of the terminals, and an initially low resistance current limiting device extending between the current-carrying extensions. The invention includes the feature that the current-limiting element including flexible conductive current-feeding arms having inner and outer end portions, the inner end portions thereof being electrically connected to the current-carrying extensions of the terminals. The outer end portions of the current-feeding arms are cantilevered and flexible relative to the inner end portions. The device further preferably includes a PTC current-limiting element sandwiched between the flexible outer end portions of the current-feeding arms. The PTC element includes a layer of a PTC material having conductive opposite faces sandwiched between the flexible outer end portions of the arms so that the PTC material carries current between the outer end portions of the current carrying arms. The layer of PTC material reaches a given trip level at an elevated current, expanding suddenly and substantially to flex the outer end portions of the current carrying arm.
U.S. Pat. No. 7,508,642 to Ye discloses a virtual II T trip criterion implemented in an electrical power distribution system to provide current-based tripping for a solid state power switching device. A first-order system model is implemented either by hardware or software to represent a rise in temperature of the electrical wire through which power is supplied. When the simulated temperature exceeds a threshold, the solid state power switching device may be tripped.
U.S. Patent Application 2007/0139842 to De'Longhi discloses a plug adapted to fit in a standard electrical outlet and supply power through a cord to an electrical device provided with a thermostat and bistable resettable switch. When one of the plug's prongs is overheated, indicating an overload or short circuit, the thermostat actuates the switch and cuts off power to the electrical device. When the malfunction is repaired, the switch is reset to restore the circuit.
U.S. Pat. No. 8,325,454 to Brugner et al. discloses an over heating detection circuit and an interrupter circuit for interrupting electrical power upon the detection of an over heating condition of an electrical plug. A heat sensitive device monitors the temperature of the electrical plug. The over heating detection circuit is connected to the heat sensitive device for detecting an over heated condition. The interruption circuit includes a disconnect switch connected to the over heating detection circuit for disconnecting electrical power upon the detection of the over heated condition in the electrical plug.
U.S. Pat. No. 8,884,773 to Wiesemann et al. discloses a shore power cord including a power supply connector electrically connected to a vehicle connector. In some cases, the vehicle connector includes features to selectively secure the vehicle connector to a vehicle power receptacle inlet. In some cases, the shore power cord includes a test module that evaluates the condition of the cord set and a power supply when the cord set is connected to the power supply.
Although the above prior art has contributed to the advancement of the art, there is a need for an elevated temperature detection and interrupter circuit for disconnecting electrical power in a power cable.
Therefore, it is an object of the present invention to provide an elevated temperature detection and interrupter circuit for a power cable for disconnecting electrical power upon the detection of the over heated condition in an electrical plug or and electrical receptacle to prevent an over heated condition.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed as being merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by modifying the invention within the scope of the invention. Accordingly other objects in a full understanding of the invention may be had by referring to the summary of the invention, the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.